Download DNA, RNA, and Protein Synthesis Notes 2006

DNA, RNA, and Protein
Synthesis Notes 2006
I. DNA
A. The Genetic Code
1. Most of the cells in living things
contain DNA.
2. DNA stores the information of life.
It contributes to making you the
person that you are.
3. DNA codes for proteins which
contribute to determining the
physical characteristics of an
organism.
4. Genetic code-how the information
of life is stored in a cell’s DNA.
B. DNA structure
1. DNA is a polymer that is formed by
units of nucleotides. All
nucleotides in DNA have 3 parts: a
5 carbon sugar (deoxyribose), a
phosphate group, and a nitrogen
containing base.
2.Nitrogen containing bases
(nitrogenous bases)
a. purines
1. adenine
2. guanine
b. pyrimidines
1. cytosine
2. thymine
3. Individual nucleotides join together
to form a molecule of DNA.
4. Nitrogenous bases do what is called
base pairing.
5. Base pairing-attraction between
complementary nitrogenous bases
that produces a force that holds the
two strands of DNA together
6. In DNA, adenine and thymine are
complementary to each other, so are
cytosine and guanine.
7. DNA molecules are in the shape of
a double helix.
a. resembles a twisted ladder
b. sugar-phosphate backbone is on
outside
c. nitrogenous bases are on the
inside
C. DNA Replication
1.The two strands that make up the
double helix of DNA are
complementary to each other. This
means that you can tell what the one
strand will look like by looking at
the other strand.
2. Each strand of DNA serves as a
pattern for a new strand to be
made.
3. Replication-the copying of DNA,
occurs prior to cell division and is
facilitated by DNA polymerases
(special enzymes).
4. During replication
a. the two strands of the double
helix get unzipped
b. matching bases are inserted
c. sugar phosphate links
are created
5. The scientists James Watson and
Francis Crick were the first to
describe the structure of DNA and
how it replicates.
II. RNA
A. RNA Structure
1. composed of a 5 carbon sugar
(ribose), a phosphate group, and a
nitrogenous base
2. differences with DNA
a. 5 carbon sugar is ribose not
deoxyribose
b. nitrogenous bases are adenine,
cytosine, guanine, and uracil
c. single stranded molecule as
opposed to double stranded
B. Types of RNA
1. messenger RNA (mRNA) –
carries information from the
DNA to the ribosomes.
2. ribosomal RNA (rRNA) - type of
RNA that makes up the major part
of the ribosome.
3. transfer RNA (tRNA) – type of
RNA that carries amino acids to
the ribosomes where the amino
acids join to form proteins.
III. Protein synthesis – the process by
which proteins are formed
A. Transcription
1. definition– the process by which
a molecule of DNA is copied into
a complementary strand of
mRNA.
2. mRNA carries the genetic code
from DNA in the nucleus to the
rribosomes in the cytoplasm.
3. RNA polymerase connects
the RNA nucleotides to each
other.
4. The synthesized strand of RNA
is complementary to one of the
DNA strands.
B. The triplet code
1. proteins are formed from
chains of amino acids
2. there are 20 different amino
acids.
3. groups of 3 consecutive
nucleotides (triplets) in mRNA
strands code for different amino
acids
4. codon- a group of three
nucleotides on an mRNA
strand that codes for an
amino acid.
5. some codons are refered to as
“stop codons” because they
end an amino acid chain.
C. Editing the RNA Message
1. In prokaryotic cells, the mRNA
molecule that is transcribed from
the gene directly serves as the
code to make proteins.
2. In eukaryotic cells, the RNA is
modified or processed before
it is used to make proteins.
3. Introns-noncoding regions in
mRNA (found in most
plant and animal cells)
4. Exons-the parts of mRNA that
are used to form proteins
5. RNA splicing-the process that
occurs before the mRNA leaves
the nucleus for translation. RNA
splicing removes the introns and
joins the exons together.
D. Translation
1. definition-the process in which
mRNA messages get decoded
into proteins.
2. The process
a. tRNA molecules have 3
bases on them that are
complementary to the
codons in mRNA. These
base sequences are
called anticodons
b. attached to each tRNA
molecule is an amino acid
specified to the codon to
which it base pairs
c. by matching the
anticodons of tRNA
to the codons of mRNA,
the correct amino acids
are put into place
d. the amino acids are then
assembled by the
ribosomes
e. the chain of amino acids
continues until a
stop codon on the mRNA
ends it.